Black finish.



UNITED STATES ATENT OFFICE.

MARK A. ATUESI' A, 015 SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

BLACK FINISF No Drawing. I

To all whom it may concern:

Be it known that I, MARK A. AT'UESTA, a citizen of the United States,residing at Schenectady, .in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in BlackFinish,of which the following is a specification.

pearance that can be easily and expeditiously produced at acomparatively low cost.

Other advantages of my finish include protection of the metal againstrust and corrosion; absence of any heavy coating liable to flake off, orto mar the sharpness of angles or impair the meshing of threads; andcertainty. and uniformity of results.

How these and other advantages can be secured will be apparent from thefollowing description of the best way of producing my finish at presentknown to me; but while the invention extends even to the specificfeatures and details of the procedure hereinafter described, it is notconfined thereto,-

its real scope being indicated in my claims. After cleaning the articlesor material to be blacked, either by pickling or by shot or sandblasting, I give them a thin coating of zinc. This I prefer to do by asherardizing process carried out in such a way that the coating shallnot exceed .0015" in thickness, thoughmaterial whose. intended use willexpose it to severe corrosive influences may be more heavily coated. Thesherardiz;

ing coat may be made thus light (as compared with that usually givenwhen articles are not to be otherwise coated) by shortening the time of.treatment, lowering the treating temperature, or

material is placed in hot charred bone dust or its equivalent to whichliquid coal tar has been added in the proportion of one quart of tar tofifteen quarts .of bone dust. One quart of the bone dust thus preparedwith tar for each eight pounds of sherardized material to be treatedrepresents good practice. Thematerial is treated with the bone dust byheating it-in a sherardizing drum to about 360 0., this temperaturebeing maintainedfor about an hour and a half. Pref- S pecification ofLetters Patent.

exceed 3 PPLY diminishing. theamount of zinc dust used. The sherardizedin which the percentage of me Patented Oct. 19, 1915 Application filedJune 9, 1915. Serial No. 33,202.

erably the temperature should not reach the melting point of zinc (419C.) or greatly (5 C., in order to avoid risk of injury to thesherardizing coat. After removal from the drum and shaking oil of thesurplus dust, the material is placed in an oven at a temperature ofabout 500 O., baked for about five minutes, and then quenched in boiledlinseed oil. Thereafter the material may be dried or freed of adherentoil either-by tumbling in it sawdust or by means ofa centrifugal oilseparator. Apparently the bone dust (which is a phosphorus containingcarbonaceous residue, consisting principally of calcium phosphate andfree carbon) gives body, the tar improves the color of the coat, as wellas its coherent and adherent properties, and the oil quenching makes itadhere more firmly; but there may .be other equally important effectsdue to the various substances.

It would appear that some reaction takes place between the sherardizingcoat (con.- sisting principally of zinc) and the carbonaceous materialemployed in the foregoing the same limit of temperature in order tosecure a black coating rather than a cementation with carbon, and, inthe case of steel, toavoid scaling. I I

In order that the best results may be secured in the practice of myinvention, I will now describe briefly the method of sherardizing that Ihave found most suit-.

able. For this operation I emtpipy zinc dust ic zinc is to 92%.-Ordinary zinc dust of commerce is usually too low in' metallic zinc, sothat Ipre fer to'use zinc powder (which is artificially producedatomized metallic zinc) and .to oxidize it to the extent indicated by apreliminary-heating in a sherardizing drum. Save for-zinc oxid, thispowder should be as pure as possible,and, especially, free fromlead,although very small quantities of by the sherardizing. Neverthe-'but it is still best to observe about silica or iron oxid do not appearto be deleterious. I prefer toheat the material in this zinc powder in alagged drum or furnace with suitable electrical heating units or coilsin its walls. The heating temperature should not Vary much beyond therange of 350 C. to 375 0., and the charge should be brought up to thistemperature as quickly as possible and kept there for about threehours,more or less,according to the thickness of the coating desired,the size of the articles, etc. After each run the zinc metal content ofthe powder should be restored to its initial proportion by admixture offresh unoxidized powder (to make up for the oxidation during that run)before being used again. A close observance of these directions insuresa. smooth, eve-n, uniform coat free from lumps, and allows its thicknessto be so accurately controlled by proper timing that bolts and nutswhose threads have been undercut sufiiciently will fit exceous binder,and subsequently quenching them in carbonaceous liquid.

2.- The method of producing arust-proof black finish on ferrous articleswhich consists in coating them with zinc, heating them in finely dividedphosphorus-containing carbonaceous material mixed with blackcarbonaceous binder, and subsequently quenching them in oil.

-3. The method of producing a rust-resisting black finish on ferrousarticles which consists in heating them in charred bonedust mixed withcarbonaceous binder and subsequently quenching them in carbonaceousliquid.

i. The method of producing a rustproof I black finish on ferrousarticles which consists in sherardizingthem, heating them in charredbone dust mixed with tarry binder at a temperature below the fusionpoint of the sherardizing coat, and subsequently quenching them in oil;

The method of producing a black finish on ferrous articles whichconsists in heating such articles in charred bone dust mixed with liquidcoal tar and subsequently quenching them in boiledlinseed oil.

In witness whereof, I have hereunto set my hand this 8th day of June,1915.

'MARK A. ATUESTA.

